Jack-up drilling rigs are typically employed for offshore energy exploration and development of offshore oil and gas fields. These drilling rigs generally float on a hull and have three or four extendable legs. In the typical situation, the drilling rig is pulled or towed to a location by one or more tug vessels. At the desired location, the drilling rig's legs are then extended to the ocean/sea floor, and the deck of the drilling rig is raised—or jacked up—out of the water. Preferably, the deck of the drilling rig is raised high enough to avoid any sea swells. The jacked-up deck of the drilling rig provides a stable structure in an environment from which a crew may perform drilling operations. These drilling rigs can withstand harsh weather conditions and may be deployed for long periods of time. Due to the nature of the work, deck space is limited and valuable.
Drilling rigs may have a cantilever system, atop which sits a fixed rig. In operation, a drilling rig is moved to a location near an oil or gas platform, a free-standing conductor, or a fixed conductor and jacked up. Then, the cantilever system is skidded out from the transom of the drilling rig and over the desired well. These cantilever systems, however, are stowed on the deck as a single unit, and take up a large portion of the limited space available.
Another type of vessel used in the oil and gas field is the derrick barge. Derrick barges are typically fitted with one or more cranes. Such cranes are typically mounted atop fixed and solid pedestals. The derrick barges, like jack-up drilling rigs, are typically pulled or towed to location. Unlike jack-up drilling rigs, however, derrick barges typically do not jack-up. Accordingly, derrick barges are subject to the pitch and roll of the sea/ocean. Thus, the derrick barge's ability to work offshore is limited by the environment in which they serve.
Yet another type of vessel used to facilitate offshore operations is a lift boat. Lift boats, like jack-up rigs, typically have three or four jack-up legs and may be elevated out of the water. Lift boats are considerably smaller than jack-up rigs, and are intended for short term deployment. These smaller vessels cannot withstand harsh weather conditions and are typically designed to move, under their own power and without the need for a tug boat, out of the way of bad weather. Accordingly, a lift boat is limited in its size and ability, and cannot function as a jack-up rig.
Additional features of the three above-identified vessels are illustrated in the following patents:
U.S. Pat. No. 4,483,644 to Johnson describes a cantilever mobile marine rig with hydraulic load equalizers. The rig includes a deck structure and a cantilever assembly skiddingly mounted on the deck structure. The hydraulic load equalizers distribute the stresses between the cantilever assembly and the structure.
U.S. Pat. No. 5,388,930 to McNease describes a method and apparatus for transporting and using a drilling apparatus or a construction crane apparatus from a single moveable vessel. In the McNease disclosure, a drilling apparatus of a construction crane apparatus is skidded onto the deck of a jack-up rig which is then floated to a remote location for use.
U.S. Pat. No. 6,257,165 to Danos, Jr. et al. describes a vessel with a movable deck. The vessel comprises a first and second pontoon, a first catamaran hull attached thereto, and a platform. The pontoons and catamaran hull float on the waters' surface, and cannot be raised. The platform is connected to the catamaran hull using jack-up legs. In this manner, the platform may be raised and lowered relative to the catamaran hull using a jacking mechanism. Danos, Jr. et al. further describes a first thruster nozzle attached to the first pontoon, the first thruster nozzle is attached in a 360 degree phase and a second thruster nozzle attached to the second pontoon, with the second thruster nozzle being movable in a 360 degree phase.
U.S. Pat. No. 6,200,069 to Miller describes a jack-up work platform. The work platform of Miller comprises a hovercraft vessel outfitted with several jack up legs. Miller states that the hovercraft can traverse environmentally sensitive terrain such as brackish and freshwater marshes without the need to dig canals that may cause or exacerbate salt water instruction. Once the drilling or exploration site is reached, the jack up legs may be lowered, lifting the work platform above the surface.
U.S. Pat. No. 6,607,331 to Sanders et al. describes a support structure for a lift crane, and in particular, to a lift crane jack-up structure, wherein the lift crane is positioned about a leg of the jack-up structure without relying upon the leg for structural support. The structure includes an above deck portion and a substructure situated below deck such that the jack-house is structurally integrated into the vessel.
U.S. Pat. No. 6,926,097 to Blake describes an offshore jack-up workover rig, which is detachably mounted on an extensible cantilevered frame. The cantilevered frame comprises a pair of parallel support beams mounted to the vessel. A pair of cantilever skid beams rests on the support beam. And, at least one hydraulic ram and cylinder is provided to drive the cantilever skid beam over the support beam.
U.S. Pat. No. 7,131,388 to Moise, II et al. describes a lift boat having recesses in the hull that receive the pads of the legs when the boat is underway. Moise, II et al. states that preferably, the total bottom surface area of the pads is preferably at least 30% of the surface area of the deck of the lift boat. Moreover, Moise describes that the total bottom surface area of the pad is large enough such that, when the boat is loaded and jacked up, the pads exert less than 7 psi on the sea floor. Moise further describes propelling the boat using two rear propellers and rudders.
Accordingly, what is needed is a modified vessel, which incorporates features of a jack-up drilling rig, a derrick barge, and a lift boat to meet the demanding requirements of offshore construction, maintenance, and demolition of oil and gas platforms, free-standing conductors, and/or fixed conductors. Preferably, the modified vessel has at least the stature of a jack-up rig with enhanced maneuverability. Further, a modified vessel having an improved crane support system which optimizes the use of deck space is needed. What is also needed is a modified vessel, which allows a work-over rig to be extended off of the transom of the modified vessel, or placed directly onto an offshore platform or structure, without taking up valuable deck space. Further needed is a removable extension system that does not take up valuable deck space. There is also a need for an improved method of selecting a location to jack-up a vessel in proximity to an offshore platform or structure, and a method of handing off a single well conductor from a jack-up rig to a modified vessel.